In the MRI apparatus, a superconducting magnet is used as a source of strong static magnetic field. For the superconducting magnet, a superconducting coil is formed by winding the superconducting wire around the coil bobbin, a thermosetting epoxy resin is filled and hardened in the gap of the superconducting wire, and then the superconducting coil is cooled to a temperature (usually, 4.2 Kelvin (−268.8° C.) that is a boiling point of liquid helium) at which the transition to the superconducting state occurs. After the cooling, a current is supplied to the superconducting coil, and a circuit called a superconducting switch is closed in a state of having reached the rated magnetic field. As a result, a closed loop state in which a permanent current flows is realized. In this manner, it is possible to maintain the superconducting state.
However, when the superconducting wire of the superconducting coil moves several micrometers or the cracking occurs in the resin that solidifies the superconducting wire in the permanent current mode, the local heat generation occurs. When the temperature of the superconducting wire exceeds a critical temperature due to the heat generation, the transition from the superconducting state to the normal conducting state (quenching) occurs. In order to prevent sudden quenching from occurring while the permanent current is held for a long time, PTL 1 proposes that the aging of the internal structure of the superconducting coil is substantially accelerated in advance by repeating the excitation and demagnetization of the superconducting magnet or making the overcurrent flow.